The present invention relates to an auxiliary device having a gripper with a plurality of nipples, each of which having an insertion part in sleeve-shaped parts, in particular for the after-cooling zone of injection molding machines for producing preforms, whereby the sleeve-shaped parts are embodied as cooling sleeves.
The invention further relates to a method for finishing preforms having a threaded part, a necking ring and a blow-molded part,                which are removed from the open mold halves in a still hot and unstable state,        wherein removal sleeves or cooling sleeves are transferred for exterior cooling,        and which, after insertion, are pressed, by compressed air, onto the interior wall of the removal sleeves or cooling sleeves within the time period of an injection molding cycle and calibrated.        
Up until two or three decades ago, a strict separation of two phases was performed for the production of preforms:
Phase 1: The preforms are formed in mold halves by injection molding by means of a hot melt and cooled down in the molds until they can be transferred to an after-cooler without suffering any damage.
Phase 2: The preforms are removed from the open injection molds and transferred to an after-cooler. In practice, three systems have prevailed:                The still hot preforms are directly transferred to cooling sleeves of an after-cooler, which is conceptually similar to a removal robot. Thereby, the after-cooler has a multiple of cooling positions in relation to the number of preforms of an injection molding cycle.        According to a second concept, the still hot preforms are removed from the open molds by a removal robot and transferred to an after-cooler.        According to a third concept, the robot function is divided into a removal gripper with water-cooled removal sleeves and a transfer gripper for the transfer to an after-cooler.        
In accordance with recent developments, attempts are made to substantially reduce the cycle time of the injection molding machine and to remove the preforms in a soft and unstable state. However, problems that were given less consideration previously have now come to the fore. Due to the physics of the cooling process, the cooling process is uneven within the walls of the preforms:                As soon as the preforms are removed from the open mold halves, thermal stress in the preforms and deformations occur.        Each engagement by robot-like grippers can lead to form damage.        The same occurs when the preforms are situated horizontally in the after-cooler.        
Thereby, each engagement in the context of the after-cooling process is extremely delicate work. A comparable example for this are robots with respect to handling raw eggs. The raw eggs must be securely held but, if possible, without applying local compressive forces that could result in breaking the egg shells.
In the production of injection-molded parts with injection molding machines, the cooling time is a determining factor for the time period of a full cycle. The first and main cooling performance still occurs in the injecting molds. Both injection mold halves are intensively water-cooled during the injection molding process so that the temperature of the injection molding parts still in the mold can be lowered from, e.g., 280° C. to a range from 70° C. to 120° C., at least in the edge layers. In the outer layers, the temperature very quickly goes lower than the so-called glass temperature of about 140° C. In the recent past, the actual injection molding process until removal of the injection-molded parts could be decreased to about 12 to 15 seconds in the case of preforms with thick walls, and to under 10 seconds in the case of preforms with thin walls, while maintaining optimal qualities with respect to the preforms. The preforms must be solidified in the mold halves to such a degree that they are captured without damage by the output auxiliary devices and transferred to a removal device. The removal device has a shape that conforms to the outer dimensions of the injection-molded parts. The intensive water-cooling in the injection mold halves occurs time-delayed from the outside to the inside, due to the physics of the cooling process. This means that the mentioned range from 70° C. to 120° C. is not uniformly achieved across the entire cross section. As a result, a quick backward-heating process from the inner area to the outer area occurs in the material cross section as soon as the intensive water cooling is interrupted by the molds. The after-cooling process is of utmost significance for two reasons. Deformations should be avoided until a stable storage state is reached. Surface defects such as pressure marks etc. should be avoided too. A cooling process that is too slow in the higher temperature range and locally harmful crystal formations due to the backward-heating process must be prevented too. The objective is a uniform amorphous state in the material of the finished preform. The rest temperature of the finished preforms should be so low that, in large packaging containers with thousands of loose poured-in parts, no pressure damage or adhesion damage can occur at the points of contact. Even after a slight backward-heating process, the injection-molded parts must not exceed a surface temperature of 40° C. The after-cooling process after removal of the hot, unstable preforms from the injection mold is very important for the dimensional stability.
WO 2004/041510 proposes an intensive cooling station as well as an after-cooler station and, for the intensive cooling station, cooling pins that can be inserted into the preforms for interior cooling. Thereby, the interior shape of the cooling sleeves conforms to the corresponding interior shape of the injection mold such that the preforms, after removal from the injection molds, can be inserted into the cooling sleeves until they fully contact the walls of the cooling sleeves, with as little play as possible. If the preforms are situated in a lying position in the first phase of the after-cooling process, then they tend to lay themselves in the downward direction onto the respective cooling sleeve part. Due to a more intensive cooling contact in the lower area, the preforms are cooled off more in the lower area so that stress occurs in the preform and so that the preform has a tendency of ovalization. If, in the first phase of the after-cooling process with shortened cooling, individual preforms in the injection molds slightly deform, then the respective deformation cannot be corrected anymore while the preforms increasingly solidify. By well directed controlling of the vacuum air and blow air, an inflation pressure can be generated in the interior of the preforms, and the preform can fully contact the entire interior wall surface of the cooling sleeve. After the preforms completely contact the interior wall area of the cooling sleeves, the surface contact is maintained for several seconds and a calibration effect is generated for each individual preform. The calibration effect leads to a high production and quality standard in the production of preforms that was not possible in the previous state of the art. In this manner, the preforms are brought into an exact form again, shortly after removal from the injection molds. Possible dimensional changes are reversed again after the first critical handling of the injection molds in the cooling sleeves. The calibration of the preforms allows for removing the preforms from the molds at still higher temperatures and for achieving a shorter injection molding cycle time.
WO 2004/041510 proposes two solution variants for generating an inflation pressure. In accordance with a first variant, a sealing ring is arranged at a cooling pin and/or at a nozzle and brought in contact with the tapered transition in the interior of a preform. In accordance with a second variant, the nozzle has ring-shaped seals which contact the face of the opening edge of the preform. Here, the inflation pressure is exerted on the entire preform. It is a disadvantage of both solutions that, in practice, a very high precision for guiding and moving all nozzles is required in the case of multiple injection molds having, e.g., 100 to 200, mold cavities.
EP 900 135 proposes a concept that is analogous to the previously mentioned second solution variant. A certain compressive force and, in addition, a sufficient form rigidity of the threaded part is required in order to seal the opening edge. So as to avoid deformations of the threaded part, the preforms must be kept in the injection molds until a higher form rigidity is achieved. However, this conflicts with shortening the injection mold cycle time.
WO 02/051614 describes an exterior cooling of the threaded part of preforms. Thereby, cooling air was blown directly onto the threaded part by way of spray nozzles. In the context of a longer cycle time, however, the exterior cooling of the thread was not necessary.
It would therefore be desirable and advantageous to provide an improved auxiliary device to obviate prior art shortcomings and to allow engagement of nipples at the product in a robot-like manner and to ensure, in the case of sleeve-shaped parts, highest qualitative parameters and maximum form accuracy of the parts in the context of the after-cooling of the preforms.